末次盛冰期西太平洋海温差异对亚洲夏季风影响的数值模拟

文章利用Zhao等的模拟结果,进一步研究了在末次盛冰期(LGM)情景下汪品先和CLIMAP两种重建海洋表面温度(SST)资料差异对亚洲夏季风的影响。模拟结果表明:在LGM情景下西太平洋海域SST资料的不同对模拟的亚洲夏季风有着十分重要的作用。夏季,与CLGM方案相比,在WLGM方案中,当热带西太平洋SST较暖时,印度地区的大气热量出现显著增加,大气热量的这种变化,使得南非高压、南印度洋经向Hadley环流加强,伴随着索马里越赤道气流加强,也导致了印度季风区纬向季风环流的加强,从而造成了印度夏季风增强、降水增多;与较暖的热带西太平洋相对应,澳大利亚高压和120°E附近越赤道气流减弱,东亚季风区20°N以南经向季风环流加强、20°N以北经向季风环流减弱,指示着一个强的南海夏季风和较弱东亚副热带大陆夏季风。     

Glacially derived material in an Inner Mongolian desert lake during Marine Isotope Stage 2

Establishing the precise timing of continental glacial dynamics and abrupt high‐latitude climate events is crucial to understanding the causes of global climate change. Here we present multi‐proxy records in a lake sediment core from arid Inner Mongolia (Wuliangsuhai Lake) that show two distinct glacially derived sedimentation events at ～26.2–21.8 and ～17.3–11.5k cal a BP. Fine sediments from the Last Glacial Maximum separate these glacially derived coarse sediments. Within these intervals, the occurrence of granite clasts at ～24–23.5, 17.3–17 and 15.6–14.1k cal a BP implies either sediment discharge by meltwater as well as strong current flow in the Yellow River and/or sediment influx through hill‐slope mass wasting and landsliding from the nearby Yin Mountains. Surface microfeatures of quartz grains and spot elemental analysis of black specks in these intervals, however, indicate that physical weathering is dominant and that the provenance of the rocks is probably from a glacial source. To the best of our knowledge, this is the first time glacier‐derived materials have been detected in any desert lake in the Yellow River basin. The occurrence of granite clasts roughly correlates with Heinrich events in the North Atlantic, suggesting synchronous ice sheet dynamics in high‐ and mid‐latitude regions during the Last Glacial period. Although our data provide unprecedented evidence for the influence of glacier‐related processes in arid Inner Mongolia, further well‐dated records are clearly needed to re‐evaluate the correlative inference drawn between granite clast layers in Wuliangsuhai Lake and Heinrich events in the North Atlantic. Copyright © 2012 John Wiley & Sons, Ltd.     

The morphology and late Quaternary paleogeomorphology of the continental shelf off Sydney,NSW

Shallow seismic-reflection profiling and proton-precession magnetometry have been conducted over the continental shelf off Sydney between Broken Bay (in the north) and Bate Bay (in the south) as well as over part of the upper continental slope in the area east of the coastline between Narrabeen and Port Hacking. In this area, four major paleodrainage channels incise the bedrock, within the coastal estuaries and on the inner and mid-shelf:

1. the Hawkesbury paleo-watercourse, which is joined offshore by four lesser paleochannels, that we call the Newport, Mona Vale, Narrabeen and Long Reef paleo-watercourses;

2. the Parramatta paleo-watercourse, which is joined by the Bondi paleo-watercourse;

3. the Botany paleo-watercourse and

4. the Georges paleo-watercourse, which is joined under the Kurnell Peninsula land isthmus by the Cooks paleo-watercourse, and then by the Hacking paleo-watercourses in Bate Bay.

Of these paleodrainages, only that of the Hawkesbury River has discernible expression at depths >120 m, the sea-level low and inferred paleo-shoreline of the Last Glacial Maximum (LGM) at ca 20 ka. Some of the lesser paleo-watercourses are manifested only at depths shallower than the ?120 m paleo-shoreline and include those of the Maroubra paleo-watercourse and the combined Manly/North Head paleo-watercourses. Paleochannels detected below the LGM shoreline are those of:

• the ancestral Hawkesbury River;

• the minor Peak paleo-watercourse east of Coogee, which is discernible at depths shallower than the ?100 m isobath and is maintained to depths greater than ?210 m; and

• the minor Island paleo-watercourse whose head terminates at ～?140 m east of Bronte, lies entirely below the LGM paleo-shoreline, and can be traced to a depth of ?260 m.

Based on the paleotopographic and sediment-infill geophysical records obtained, 10 stages in the evolution of the paleo-watercourses are proposed.     

GEOTHERMICS GEOLOGY

正20140958 Mei Huicheng(No.915GeologicalBrigade,Jiangxi Bureau of Geology and Mineral Resources,Nanchang 330002,China);Li Zhongshe Geological Features and Causes of the Huihuang Geotherm in Xiushui,Jiangxi Province(Journal of Geological Hazards and     

A 16 000‐year record of vegetational change in south‐western Alaska as inferred from plant macrofossils and pollen

Pollen and macrofossil analyses of a sediment core from Beaver Pond (60° 37′ 14″ N, 154° 19′ W, 579 m a.s.l.) reveal a record of regional and local postglacial vegetation change in south‐western Alaska. The chronology is based on five AMS (accelerator mass spectrometry) ¹⁴C ages obtained from terrestrial plant macrofossils. Pollen and macrofossil records suggest that open herb and shrub tundra with e.g. Poaceae, Cyperaceae, Artemisia, Vaccinium and Salix prevailed on the landscape before ca. 14 000 cal a BP. The shift from herb‐ to shrub‐dominated tundra (Salix, subsequent Betula expansion) possibly reflects climatic warming at the beginning of the Bølling period at ca. 14 700–14 500 and around 13 500 cal a BP. Vegetation (Betula shrub tundra) remained relatively stable until the early Holocene. Macrofossil influx estimates provide evidence for greater biomass in Betula shrub tundra during the early postglacial period than today. Charcoal accumulation rates suggest tundra fire activity was probably greater from ca. 12 500 to 10 500 cal a BP, similar to results from elsewhere in Alaska. The pollen and macrofossil records of Beaver Pond suggest the prevalence of low shrub tundra (shrub Betula, Betula nana, Vaccinium, Ledum palustre, Ericaceae) and tall shrub tundra (Alnus viridis ssp. crispa, Salix) between 10 000 and 4000 cal a BP. This Holocene vegetation type is comparable with that of the modern treeless wet and moist tundra in south‐western Alaska. The expansion of Picea glauca occurred ～4000 cal a BP, much later than that of A. viridis (ssp. crispa), whereas in central and eastern Alaska Picea glauca expanded prior to or coincident with Alnus (viridis). At sites located only 200–400 km north‐east of Beaver Pond (Farewell and Wien lakes), Picea glauca and Betula forests expanded 8000–6000 cal a BP. Unfavourable climatic conditions and soil properties may have inhibited the expansion and establishment of Picea across south‐west Alaska during the mid and late Holocene. Copyright © 2011 John Wiley & Sons, Ltd.     

Late Quaternary environmental phases in the Eastern Cape and adjacent Plettenberg Bay-Knysna region and Little Karoo, South Africa

Four major climato-environmental phases have been identified in the Eastern Cape, Plettenberg Bay-Knysna region and Little Karoo between somewhat before ∼40 000 cal. a BP and the present: the Birnam Interstadial from before 40 000 cal. a BP until ∼24 000 cal. a BP; the Bottelnek Stadial (apparently equating with the Last Glacial Maximum) from ∼24 000 cal. a BP until before ∼18 350 cal. a BP; the Aliwal North (apparently equating with the Late Glacial) from before ∼18 350 cal. a BP until ∼11 000 cal. a BP; the Dinorben (apparently equating with the Holocene) from ∼11 000 cal. a BP until the present. The evidence for, and the characteristics of, these phases is briefly described.     

Geological perspectives on the Monte Verde archeological site in Chile and pre-Clovis coastal migration in the Americas

Discovery of the Monte Verde archeological site in Chile overturned the previous consensus that the first Americans into the New World from Asia were the makers of Clovis projectile points, and rejuvenated the hypothesis that migration through the Americas occurred largely on portions of the Pacific continental shelf exposed by Pleistocene drawdown in eustatic sea level. The postulate of travel along a paleoshoreline now hidden underwater is an attractive means to posit pre-Clovis human movement southward from Beringia to Chile without leaving traces of migration onshore. Geologic analyses of the Pleistocene paleoenvironment at Monte Verde and of the morphology of the potential migration route along the continental shelf raise questions that have not been fully addressed. The periglacial setting of Monte Verde may call its antiquity into question and the narrowness of the Pacific continental shelf of the Americas makes it unlikely that people could travel the length of the Americas without impacting ground still onshore and no farther inland than Monte Verde itself. Geological perspectives on Monte Verde and coastal migration jointly suggest that the Clovis-first hypothesis for peopling the New World may have been abandoned prematurely.     

Submerged reefal deposits near a present‐day northern limit of coral reef formation in the northern Ryukyu Island Arc,northwestern Pacific Ocean

High‐resolution single‐channel seismic reflection surveys were carried out in the northern Ryukyu Island Arc during an NT05‐14 cruise of the R/V Natsushima. The survey area is located northeast of Amami Oshima and southwest of Kikai Shima immediately south of the current northern limit of coral reef formation in the northwestern Pacific Ocean. The main purpose of the surveys was to ascertain whether coral reefs formed during glacial periods and, if so, to determine their three‐dimensional distribution. We collected 784 km of high‐resolution single‐channel seismic data during the cruise. The acoustic basement is clearly observed under the Amami Spur, off Amami Oshima. The seismic profiles show two anticlines, each with an axis trending northeast to southwest. Thin Quaternary stratified sediment overlies the acoustic basement in the northwestern and southeastern slope areas, as well as between the anticlinal axes. The stratified sediment can be divided into several sedimentary units. The mound‐shaped reflections are found within the stratified sedimentary units in the central to eastern parts of the spur. Because the mound‐shaped reflections are characterized by strong reflections and chaotic internal structures in profiles, they are considered biogenic ‘reefs’ or banks consisting of coarse‐grained bioclasts. They overlie the acoustic basement or stratified sediment and reach 15 m in thickness and 400 m in width. In contrast, irregularly shaped topographic highs were detected at the shelf edge southwest off Kikai Shima, which are likely to be remnants of coral reefs formed during the last glacial period. Our seismic data indicate probable coral reef formation at low stands during glacial stages, such as the Last Glacial Maximum, even in the northern Central Ryukyus. The occurrence of drowned reefs may indicate that their growth rate was not sufficient to keep up with a rapid rise in sealevel after a glacial period.     

末次盛冰期以来长江下关-栖霞山段下切深度及沉积旋回

选择长江下关-栖霞山段作为研究河段,搜集了南京长江大桥、四桥附近的76个钻孔资料.根据地质钻孔资料,绘制南京长江大桥和长江四桥附近长江古河槽地质剖面.在拟建长江四桥附近的4个钻孔采集了沉积物样品,在-59.33 m深度上河床相沉积物的年代为(14 682±110)a BP,据此判断位于该沉积层下部的上一期沉积旋回应形成...